The industry’s view of greenhouse gas (GHG) emissions and air pollutants associated with different shipping fuels depends on how organizations like the International Maritime Organization (IMO) analyze them. However, the climate and health impacts of a fuel do not change depending on the emissions analysis chosen.
Well-to-wake emissions analysis is similar to well-to-wheel emissions analysis for road vehicles and is also known as life cycle analysis. It includes emissions related to every stage in the life cycle of a fuel — from its production until it is used to fuel a vessel.
A shipping fuel can be classified as carbon-neutral in this approach and still release tailpipe emissions if its overall carbon emissions are net-zero when considering the entire life cycle of the fuel.
Many experts argue that this is the only way to accurately measure the climate and health impacts of a fuel. However, many in the shipping industry push for the tank-to-wake or tank-to-wheel approach to measure emissions.
This approach takes into account the emissions that result from burning or using a fuel once it is already in the tank. How a fuel is produced and transported to get to a vessel’s tank is not included in this analysis.
To qualify as a carbon-neutral fuel using this approach, the fuel has to have zero tailpipe emissions. Battery-electric and hydrogen are two of the most common zero-tailpipe-emissions fuels considered when taking a tank-to-wake approach.
A fuel such as renewable natural gas that can be carbon-negative over its life cycle would not qualify as carbon-neutral using this approach since natural gas emits GHGs as it powers a vessel.
Why does the difference matter?
The short answer is that completely different alternative fuels could be favored and subsidized depending on the emissions analysis used.
Using a tank-to-wake approach could misrepresent the total climate and health impacts of shipping fuels. While carbon-neutral tank-to-wake fuels such as hydrogen produce zero tailpipe emissions, the way hydrogen is produced has a large impact on its life cycle emissions.
The majority of hydrogen today, 95% according to the U.S. Department of Energy, is gray hydrogen; it is produced using natural gas and releases GHGs in the process. Green hydrogen is produced using renewable electricity to separate water into hydrogen and oxygen, releasing oxygen as the only byproduct.
Using a tank-to-wake approach, all hydrogen, whether produced using natural gas or renewable electricity, would be viewed as a carbon-neutral fuel because it doesn’t release GHGs when it’s used to power a vessel.
Some experts view this as inaccurate because gray hydrogen still results in GHG emissions — it just happens during production before the fuel gets to the tank.
Using a well-to-wake approach, green hydrogen would be a carbon-neutral fuel and gray hydrogen would not.
The IMO has been debating whether to take a tank-to-wake or well-to-wake approach when it comes to approving carbon-neutral fuels for the future.
“Right now, the IMO says that our authority or responsibility is for emissions on a tank-to-wake basis,” Gregory Dolan, CEO at the Methanol Institute, told FreightWaves. “If they’re looking at achieving their GHG ambitions, and it’s just a tank-to-wake basis, that means for the ship operator, you can only use the zero-carbon fuels, which would be ammonia or hydrogen or batteries.
“But the interesting thing there is that there’s no obligation that that ammonia or hydrogen is coming from renewable feedstocks. It can be produced from natural gas because their obligation stops when it gets into the tank. If we look at the GHG ambition from a well-to-wake basis, then you have the ability to bring the whole fuel chain into the discussion to provide low-carbon and net-carbon-neutral fuels for the shipping sector, which makes a lot more sense,” Dolan said.
Dolan noted that it doesn’t make sense to disqualify carbon-neutral fuels such as renewable natural gas or renewable methanol because they have the ability to reduce shipping emissions now, while the industry waits for zero-emission fuel technology to catch up.
“We need to make sure that the IMO policy framework doesn’t preclude you from using net-carbon-neutral fuels in the future,” Dolan said.